Image display and method for displaying image

ABSTRACT

At the time when displaying moving images using liquid crystal panels and others, there is such a problem that tail streaks occur, and resultantly image degradation is caused. In order to solve this problem, an echo suppression circuit  100  divides a video signal into a pair composed of two successive frames for comparison between these two frames in signal level for the purpose of suppressing an echo phenomenon occurring when a liquid crystal panel  108  displays video signals including moving images. If these two frames are not the same in signal level, the signal is accordingly so corrected as to equalize the signal level of those. Based on the video signals and others corrected by the echo suppression circuit  100,  a controller  102  operates the liquid crystal panel with Alternating-Current drive through a source driver  104  and a gate driver  106.  As such, the drive voltage used to operate the liquid crystal panel with AC drive is so adjusted as to be balanced between positive and negative. In this manner, the tail streaks are prevented when displaying moving images.

TECHNICAL FIELD

[0001] The present invention relates to image display apparatuses and,more specifically, to image display apparatuses for displaying imagesbased on input video signals, and especially these are preferablyapplicable when displaying moving images on liquid crystal displayapparatuses.

BACKGROUND ART

[0002]FIG. 31 is a block diagram showing the structure of a conventionalliquid crystal display apparatus. In FIG. 31, the conventional liquidcrystal display apparatus includes a controller 910, a source driver911, a gate driver 912, and an IPS-type liquid crystal panel 913. Thecontroller 910 performs, as a main role, timing control of the sourcedriver 911 and the gate driver 912, and Alternating-Current drivecontrol of the IPS-type liquid crystal panel 913.

[0003] In the below, described is the AC drive of the liquid crystalpanel. In the liquid crystal panel, a liquid crystal material is used toseal between two electrodes on a pixel basis so as to change the voltageto be applied between these electrodes. Thereby, liquid crystalmolecules are aligned differently, accordingly the optical property ischanged, and image display is thus performed. Generally, in a TN(Twisted Nematic)-type liquid crystal panel, if a Direct-Current isapplied thereto as a driving voltage, ions in the liquid crystalmaterial moves closer to the electrodes, and resultantly a phenomenoncalled sticking-image occurs with some display images stayed. This isthe reason why the liquid crystal panel often operates with AC drive,and is generally driven in AC waveforms in which the polarity alternatesin synchronization with a vertical synchronizing signal of the videosignal. FIG. 32 is a diagram showing a drive voltage waveform of, undersuch a conventional AC drive method, a test pattern of still imagesshowing gray, white, and gray in the horizontal direction. The lateralaxis is a space axis, that is, indicating pixel positions in thehorizontal direction. Because of operation with AC drive, the polarityof the drive waveform alternates on a frame basis, that is, between anodd-numbered frame and an even-numbered frame. Here, as shown in FIG.32, the polarity of the drive waveform also alternates between anyhorizontally adjacent pixels, which is called dot reverse, or columnreverse, and is one popular method used to reduce flicker oftenoccurring at the time of AC drive.

[0004] On the other hand, as a technique for improving the viewing angleperformance of liquid crystal displays, liquid crystal panels of anin-plane switching type (hereinafter, referred to as IPS (in-PlaneSwitching) type) have been recently developed.

[0005]FIG. 33 are diagrams showing the structure of such an IPS-typeliquid crystal panel, and specifically, FIG. 33(a) is a diagram viewedfrom a direction perpendicular to its display surface, while FIG. 33(b)shows a section view. As shown in FIG. 33, in the IPS-type liquidcrystal panel, two electrodes for driving liquid crystal, i.e., a commonelectrode 921, and a drain electrode 922 which is connected to a sourceline 920 through a pixel transistor 923, are in such a comblikestructure as occluding each other on the same surface of a glasssubstrate 924. In the IPS-type liquid crystal panel, switching takesplace with respect to the liquid crystal of a liquid crystal layer 927by a horizontal electric field generated between those electrodes,thereby advantageously realizing the property of a quite wide viewingangle. Here, because the liquid crystal is rather slow in responsespeed, the IPS-type liquid crystal panels are now mainly used as displaypanels for still images exemplified by monitors of personal computers.With the improvement of the IPS-type liquid panels and their relatingtechnologies, the IPS-type liquid crystal panels are becoming applicableto display moving images such as television signals.

[0006] The issue here is, if a liquid crystal display apparatusincluding a conventional IPS-type liquid crystal panel displays movingimages such as television signals, there surely arises a problem due toliquid crystal being slow in response speed, and yet the inventors havefound another problem through their study that, movement of displayingobjects, patterns, and others in the moving images result in tailstreaks, causing image degradation of the region to which those moved.

[0007] In the below, by referring to FIGS. 33 to 37, described in detailis a mechanism why such a new problem of image degradation occurs ifmoving images are displayed on the IPS-type liquid crystal panel in theconventional liquid crystal display apparatus.

[0008] Prior thereto, described first is the electrode structure of theIPS-type liquid crystal panel in comparison with that of the generalTN-type liquid crystal panel.

[0009] Generally, in the TN-type liquid crystal panel, a planartransparent electrode (ITO) is provided for each of glass substrateswhich are so placed as to face each other. With such a structure, theplanar ITO works as a stopper when an insulator film over the ITO isremoved in the manufacturing process, whereby etching can be done withno overetching caused. In the IPS-type liquid crystal panel, on theother hand, as shown in FIG. 33, pixel electrodes which are in acomblike structure (e.g., Al, Cr), that is, the common electrode 921 andthe drain electrode 922 are so placed as to occlude each other on thesame surface of the glass substrate. With such a structure, wheninsulator films over those pixel electrodes, that is, a gate insulatorfilm 925 and a protection insulator film 926, are removed in themanufacturing process, such electrodes as the common electrode 921 andthe drain electrode 922 work as a stopper for their own part, but thereis none working as a stopper for a part between the common electrode 921and the drain electrode 922. Thus, without correct control over theetching speed, there is a possibility for overetching. This is thereason why the insulator films over the pixel electrodes are often notremoved in the IPS-type liquid crystal panel, that is, the pixelelectrodes remain covered by the insulator films. This is one cause ofthe tail streaks mentioned in the above.

[0010]FIG. 34 are diagrams showing drive voltage waveforms of theconventional liquid crystal display apparatus including the IPS-typeliquid crystal panel in the case where a test pattern showing white,gray, and white is moved by two pixels rightward on a frame basis. Inthose drawings each corresponding to a frame, the lateral axes indicatepixel positions in the horizontal direction (space axes), the verticalaxes indicate the drive voltage, and the frames are arrangedlongitudinally in order (discrete time). As already described byreferring to FIG. 32, with AC drive, the polarity alternates on a framebasis in the drive voltage waveform, and further with column reverse,the polarity alternates on a pixel basis in the horizontal direction inthe drive voltage waveform.

[0011] Here, in FIG. 34, focusing on a pixel A shown therein, time-baserepresentation of any change observed in the drive voltage will lead toa diagram shown in FIG. 35(a). As indicated by a thick line of FIG.35(a), DC components (low frequency components) of the voltage appliedto the electrodes become out of balance when the test pattern passesthrough. In other words, at the time when the test pattern passesthrough, applied to the electrodes of the IPS-type liquid crystal panelis the DC voltage.

[0012] As described in the foregoing, the electrodes of the IPS-typeliquid crystal panel are each covered by an insulator film (SiNx),therefore with a DC voltage applied to the electrodes as such,polarization occurs in the insulator films. FIG. 36 is a model diagramshowing how polarization occurs as a result of DC voltage application,(−) to the common electrode 921, and (+) to the drain electrode 922. Asshown in FIG. 36, DC voltage application to the IPS-type liquid crystalpanel causes ions in its liquid crystal layer to move, and due toresultant uneven distribution of ions, polarization occurs both in theliquid crystal layer and the insulator films covering the electrodes. Asa result of such polarization, electric field components are generatedso that the electric field applied to the liquid crystal layer iscancelled out thereby. Moreover, the electric field components generatedas such keep affecting the electric field applied to the liquid crystalfor the duration until polarization level is lowered.

[0013]FIG. 35(b) is a diagram showing an electric field applied to theliquid crystal of the focusing pixel A. As indicated by a thick line inFIG. 35(b), due to polarization resulted from an electrode voltage addedwith DC components, such an electric field component as canceling outthe DC components affects an electric field to be applied to the liquidcrystal during a pattern display period and thereafter. Here, focusingon the electric field especially after the pattern has passed through,in frames after the pattern has passed through, the voltage to beoriginally applied to the liquid crystal of the pixel A is the oneshowing no change in absolute value as shown in FIG. 35(a). However, asshown in FIG. 35(b), actually applied thereto is such a voltage asincreasing and decreasing in absolute value on a frame basis. As aresult, AC drive gets out of balance between positive and negative,causing flicker. As described above, under AC drive, the polarityalternates in synchronization with the vertical synchronizing signal.Accordingly, such flicker occurs in half of the frequency component ofthe vertical synchronizing signal.

[0014] Such flicker increases in proportion to the size of the DCcomponent and the time when the DC component was applied. As an example,first displaying white for a positive frame and black for a negativeframe sequentially for two seconds each, and then displaying grayresultantly occurs flicker visible even to the naked eyes. Also, even ifthe flicker occurred thereby is in such a level as not being visible tothe naked eyes when the line of sight is fixed, it may become visibleonce the line of sight is changed. This is explainable by the human eyesas being a sensory organ sensitive to the amount of spatial and temporalchanges. When the line of sight is fixed, only the amount of temporalchange in brightness becomes sensory stimulation, but when the line ofsight is changed, in addition to the amount of temporal change inbrightness, the amount of spatial change in brightness becomes also thesensory stimulation. For example, as shown in FIG. 37, in a displayscreen 914 of the IPS-type liquid crystal panel, if an exemplary testpattern of a white BOX 915 is moved leftward within a gray background916, the human eyes follow this movement. Since synchronization isestablished between the movement of the test pattern and flicker, asindicated by arrows in FIG. 38, the line of sight has a directionalproperty in the temporal and spatial direction, and as a result, flickeroccurs as if a pattern of streaks is moving. As a result, such a tailecho 917 as shown in FIG. 37 is perceived. As such, unlike generalafterglow, the tail echo 917 looks as the pattern of streaks, causingconsiderable image degradation of the moving images.

[0015] Here, as described in the foregoing, one cause of the tail echo917 is uneven distribution of ions (liquid crystal polarization) as aresult of DC voltage application. This polarization occurs as a resultof impurity ions in the liquid crystal panel moving in response to theelectric field. Accordingly, the polarization level is increased as thedensity of such impurity ions is increased in the liquid crystal panel.

[0016] Conventionally, in order to increase the response speed of aliquid crystal material used for the IPS system, its viscosity has beenon a downward path. Further, in order to lower the drive voltage, Δε(anisotropic dielectric constant) has been on an upward path. Throughsuch development, the liquid crystal material for the IPS systemgenerally includes CN liquid crystal, or the liquid crystal material tobe used therefor is high in ε (permittivity). However, with such aliquid crystal material including CN liquid crystal or being high in ε,impurity ions are to be easily captured in the liquid crystal. As aresult, as already described, polarization is to be occurred easily sothat electrical charge on the resultant interface is increased.

[0017] Moreover, for the purpose of reducing stiucking-image, forexample, the liquid crystal panel may be filled with liquid crystal of alow resistance or provided with an orientation film, the liquid crystalpanel may be irradiated with UV ray, or the liquid crystal therein maybe mixed with any additive. If these are the cases, however, the iondensity in the liquid crystal is resultantly increased so that the abovedescribed echo phenomenon occurs more apparently, considerably degradingthe quality of the moving images.

[0018] Therefore, an object of the present invention is to provide aliquid crystal display apparatus and method in which no echo phenomenonis occurred even if moving images are displayed using a liquid crystalpanel.

DISCLOSURE OF THE INVENTION

[0019] To achieve the above object, the present invention has thefollowing aspects.

[0020] A first aspect of the present invention is directed to an imagedisplay apparatus for displaying an image based on an input videosignal, comprising:

[0021] a display device for outputting image lights according to avoltage to be applied;

[0022] drive means for driving the display device by switching the drivevoltage between positive and negative for application based on the inputvideo signal; and

[0023] means for suppressing a polarization phenomenon in the displaydevice.

[0024] As described above, in the first aspect, the echo phenomenonoccurring when moving images are displayed can be suppressed bypreventing the polarization phenomenon in the display device.

[0025] According to a second aspect, in the first aspect, the means forsuppressing the polarization phenomenon is adjustment means foradjusting the drive voltage by correcting the input video signal or thedrive voltage so that absolute values of the drive voltage betweenpositive and negative become closer in at least any two successiveframes.

[0026] As described above, in the second aspect, the drive voltage canbe better balanced between positive and negative by adjusting absolutevalues of the positive and negative drive voltages to be closer. As aresult, ions are not easily distributed unevenly and polarization hardlyoccurs in the insulator film, thereby suppressing the echo phenomenon.

[0027] According to a third aspect, in the second aspect, when anabsolute value of the drive voltage in an n-th frame of a signal beingnormal to the input video signal is different from an absolute value ofthe drive voltage in an n+1-th frame or in an n−1-th frame, theadjustment means adjusts the drive voltage of any one of the n+1-thframe, the n−1-th frame, or the n-th frame.

[0028] As described above, in the third aspect, since the drive voltageis adjusted by referring to both a preceding frame and a subsequentframe, whereby adjustment can be done more optimally.

[0029] According to a fourth aspect, in the third aspect, the adjustmentmeans adjusts both of the n+1-th frame and the n−1-th frame.

[0030] As described above, in the fourth aspect, both of the precedingframe and the subsequent frame are subjected to drive voltageadjustment. Therefore, such adjustment can be done more optimallydepending on the video signal, and as a result, the resultantlycorrected moving images look smoother.

[0031] According to a fifth aspect, in the third aspect, when adjustingthe drive voltage, the adjustment means holds a maximum value or aminimum value.

[0032] As described above, in the fifth aspect, by leaving the maximumvalue or the minimum value as it is without correcting the same, theoriginal video signal can retain its contrast.

[0033] According to a sixth aspect, in the third aspect, when adjustingthe drive voltage, the adjusting means holds a sum of the absolutevalues or a square sum of the absolute values of the n+1-th frame, then−1-th frame, and the n-th frame.

[0034] As described above, in the sixth aspect, by equalizing, in termsof time, average values of the absolute values of the drive voltagebefore and after correction, correction can be done with littleinfluence, and the resultant images look smoother.

[0035] According to a seventh aspect, in the second aspect, in the twosuccessive frames the polarity of the drive voltage applied thereto isdifferent from each other, the adjustment means adjusts the drivevoltage to make a difference of the absolute values of the drive voltageto be ½ of a maximum drive voltage or smaller.

[0036] As described above, in the seventh aspect, the drive voltage isso corrected as to be in balance between positive and negative, wherebyecho phenomenon can be restrained to a greater degree.

[0037] According to an eighth aspect, in the seventh aspect, theadjustment means adjusts the drive voltage to make the difference of theabsolute values of the drive voltage to be {fraction (1/10)} of themaximum drive voltage or smaller.

[0038] As described above, in the eighth aspect, the drive voltage is socorrected as to be in much better balance between positive and negative,and thus the echo phenomenon can be suppressed to such a level as not tobe perceivable by the naked eyes.

[0039] According to a ninth aspect, in the eighth aspect, the adjustmentmeans adjusts the drive voltage when, prior to adjustment, thedifference of the absolute values of the drive voltage is exceeding{fraction (1/10)} of the maximum drive voltage.

[0040] As described above, in the ninth aspect, only when the echophenomenon is to be observed by the naked eyes, the drive voltage can becorrected.

[0041] According to a tenth aspect, in the first aspect, the drive meansdivides one vertical scanning period of the input video signal into afirst sub period and a second sub period, and the drive voltage appliedto the sub periods is different in polarity.

[0042] As described above, in the tenth aspect, by adjustably balancingthe drive voltage between positive and negative on the basis of verticalscanning period, the echo phenomenon can be restrained.

[0043] According to an eleventh aspect, in the tenth aspect, the drivemeans outputs the same video signal in the first sub period and thesecond sub period.

[0044] As described above, in the eleventh aspect, the drive voltage canbe adjusted only by switching the polarity of the drive voltage betweenthe first sub period and the second sub period. Therefore, the structurecan be simplified.

[0045] According to a twelfth aspect, in the tenth aspect, the first subperiod and the second sub period are the same in length.

[0046] As described above, in the twelfth aspect, the drive voltage canbe adjusted only by simply increasing the signal speed. Therefore, thestructure can be simplified.

[0047] According to a thirteenth aspect, in the tenth aspect, the firstsub period and the second sub period are not the same in length.

[0048] As described above, in the thirteenth aspect, such adjustment canbecome possible as considering the speed of the ions moving in theliquid crystal, for example.

[0049] According to a fourteenth aspect, in the tenth aspect, the drivemeans includes division means for dividing the one vertical scanningperiod of the input video signal into the first sub period and thesecond sub period.

[0050] As described above, in the fourteenth aspect, each verticalscanning period of the input video signal can be divided, for output,into the first sub period and the second sub period. Therefore, only byswitching the polarity of these signals, the drive voltage can beadjusted.

[0051] According to a fifteenth aspect, in the fourteenth aspect, thedivision means includes means for temporarily storing the input videosignal.

[0052] As described above, in the fifteenth aspect, even with high-speeddrive, the reliability will not be lowered through division.

[0053] According to a sixteenth aspect, in the fourteenth aspect, thedivision means includes means for delaying the input video signal by alength of time equal to or shorter than the one vertical scanningperiod.

[0054] As described above, in the sixteenth aspect, the division meanscan be realized at lower cost.

[0055] According to a seventeenth aspect, in the fourteenth aspect,conversion means is further comprised for converting the input videosignal into a data display signal for driving the display device,wherein

[0056] in a process for converting the input video signal into the datadisplay signal, the conversion means divides the one vertical scanningperiod of the input video signal into the first sub period and thesecond sub period.

[0057] As described above, in the seventeenth aspect, the number ofrequired constituents can be reduced, and thus the liquid crystaldisplay apparatus can be realized at relatively low cost.

[0058] According to an eighteenth aspect, in the first aspect, the drivemeans divides one vertical scanning period of the input video signalinto a first sub period and a second sub period, and outputs the inputvideo signal in the first sub period, and outputs a compensation signalin the second sub period.

[0059] As described above, in the eighteenth aspect, irrelevant to theinput video signal, a compensation signal which affects image displaynot that much is inserted to each vertical scanning period. In thismanner, uneven ion distribution is eased, and the echo phenomenon can berestrained.

[0060] According to a nineteenth aspect, in the eighteenth aspect, hesecond sub period is shorter than the first sub period.

[0061] As described above, in the nineteenth aspect, the screen can beprevented from being lowered in brightness due to the compensationsignal inserted thereto.

[0062] According to a twentieth aspect, in the eighteenth aspect, thedrive voltage in the second sub period is a voltage of a pedestal levelor lower when the display device is a normally black type, and when thedisplay device is a normally white type, a voltage of the pedestal levelor higher.

[0063] As described above, in the twentieth aspect, uneven iondistribution can be cancelled sooner without, nearly, affecting imagedisplay, whereby resultant effects by such improvement can be enhanced.

[0064] According to a twenty-first aspect, in the twentieth aspect, thedisplay device is a normally black type, and the drive voltage in thesecond sub period is 0V.

[0065] As described above, in the twenty-first aspect, uneven iondistribution can be cancelled sooner without, nearly, affecting imagedisplay, whereby resultant effects by such improvement can be enhanced.

[0066] According to a twenty-second aspect, in the eighteenth aspect,the drive voltage in the second sub period is applied to a plurality ofscanning lines at one time.

[0067] As described above, in the twenty-second aspect, the time takenfor scanning can be shortened by reducing the scanning time taken forwriting of the compensation signal.

[0068] According to a twenty-third aspect, in the first aspect, thedrive means

[0069] scans, in an n-th frame, odd-numbered scanning lines for a datasignal, and even-numbered scanning lines for a compensation signal, and

[0070] scans, in an n+1-th frame, the odd-numbered scanning lines forthe compensation signal, and the even-numbered lines for the datasignal.

[0071] As described above, in the twenty-third aspect, by inserting acompensation signal to all of the pixels on a frame basis, uneven iondistribution can be eased, and the echo phenomenon can be suppressed.Further, the timing for displaying the compensation signal may beshifted by one frame depending on whether the scanning line isodd-numbered or even-numbered. This prevents the screen gets blackenedin its entirely for every other frame due to the compensation signal,for example. Moreover, when the video signal is an interlace signal,there is no need to convert it to a progressive signal. Therefore, theimage display apparatus can be realized at relatively low cost.

[0072] According to a twenty-fourth aspect, in the first aspect, duringone vertical scanning period of the input video signal, aftersequentially scanning either ones of odd-numbered scanning lines andeven-numbered scanning lines, the drive means sequentially scans thescanning line.

[0073] As described above, in the twenty-fourth aspect, since aperiodical change in brightness being a cause of the echo phenomenon isshifted by a half period for any adjacent scanning lines, the echophenomenon becomes not perceivable.

[0074] According to a twenty-fifth aspect, in the first aspect, thedrive means applies the drive voltage of the same polarity withoutpolarity reverse to at least any two successive frames.

[0075] As described above, in the twenty-fifth aspect, the drive voltageis corrected to be in better balance between positive and negative, andthus the echo phenomenon can be restrained.

[0076] According to a twenty-sixth aspect, in the twenty-fifth aspect,the drive means applies such a drive voltage as alternating the polarityfor every two frames.

[0077] As described above, in the twenty-sixth aspect, the drive voltageis corrected to be in better balance between positive and negative, andthus the echo phenomenon can be restrained.

[0078] According to a twenty-seventh aspect, in the twenty-fifth aspect,the drive means applies the drive voltage of the same polarity betweenany two successive frames once for every n frames.

[0079] As described above, in the twenty-seventh aspect, the drivevoltage is corrected to be in better balance between positive andnegative, and thus the echo phenomenon can be restrained.

[0080] According to a twenty-eighth aspect, in the first aspect, thedisplay device includes:

[0081] liquid crystal; and

[0082] an orientation film, and

[0083] a combination of the liquid crystal and the orientation film is acombination to make a voltage holding ratio 98% or higher.

[0084] As described above, in the twenty-eighth aspect, the echophenomenon can be prevented from occurring.

[0085] According to a twenty-ninth aspect, in the first aspect, thedisplay device includes:

[0086] liquid crystal; and

[0087] an orientation film, and

[0088] as said means for suppressing the polarity phenomenon, the liquidcrystal includes 1 wt % or less of a CN compound, and the orientationfilm does not include a high polymer whose conjugated length is sevenatoms or more.

[0089] As described above, in the twenty-ninth aspect, the echophenomenon can be prevented from occurring.

[0090] According to a thirtieth aspect, in the first aspect, the displaydevice includes:

[0091] liquid crystal;

[0092] an orientation film; and

[0093] a pixel electrode and a common electrode for applying the voltageto the liquid crystal, and

[0094] at least a part of the pixel electrode and the common electrodeapplies the voltage to the liquid crystal only via the orientation film.

[0095] As described above, in the thirtieth aspect, electric chargewhich is the cause of the echo phenomenon becomes easily absorbed intothe electrode. Accordingly, the echo phenomenon can be prevented fromoccurring.

[0096] According to a thirty-first aspect, in any one of the first tothirtieth aspects, the display device includes:

[0097] liquid crystal; and

[0098] an electrode for applying the voltage to the liquid crystal, and

[0099] a part of the liquid crystal is driven in a state that there isnone of the electrode in the vicinity thereof.

[0100] As described above, in the thirty-first aspect, if the liquidcrystal has any region including no electrode in the vicinity as in theregion between electrodes in the IPS-type liquid crystal panel, forexample, electric charge which is a cause of the echo phenomenon maystay without being absorbed into the electrodes. Even if these displaydevices are to be used, the echo phenomenon can be successfullysuppressed.

[0101] According to a thirty-second aspect, in any one of the first tothirtieth aspects, the display device includes:

[0102] liquid crystal; and

[0103] a pixel electrode and a common electrode for applying the voltageto the liquid crystal, and

[0104] the liquid crystal is driven by an electric field which isgenerated between the pixel electrode and the common electrode, and isalmost parallel to a substrate.

[0105] As described above, in the thirty-second aspect, the echophenomenon can be successfully suppressed even with the IPS-type liquidcrystal panel in which electric charge which is a cause of the echophenomenon may stay without being absorbed into the electrodes.

[0106] According to a thirty-third aspect, in any one of the first totwenty-seventh aspects, the display device is made of a material withwhich an echo phenomenon easily occurs.

[0107] As described above, in the thirty-third aspect, the echophenomenon can be successfully suppressed even with the display devicemade of a material with which the echo phenomenon easily occurs.

[0108] A thirty-fourth aspect is directed to an image display method fordisplaying an image by driving a display device based on an input videosignal, comprising:

[0109] a drive step of driving the display device by switching a drivevoltage between positive and negative for application based on the inputvideo signal; and

[0110] an adjusting step of adjusting the drive voltage by correctingthe input video signal or the drive voltage so that absolute values ofthe drive voltage between positive and negative become closer in atleast any two successive frames.

[0111] As described above, in the thirty-fourth aspect, the drivevoltage can be better balanced between positive and negative byadjusting absolute values of the positive and negative drive voltages tobe closer. As a result, ions are not easily distributed unevenly andpolarization hardly occurs in the insulator film, thereby suppressingthe echo phenomenon.

[0112] A thirty-fifth aspect is directed to an image display method fordisplaying an image by driving a display device based on an input videosignal, comprising

[0113] a drive step of driving the display device by switching a drivevoltage between positive and negative for application based on the inputvideo signal, wherein

[0114] the drive step divides one vertical scanning period of the inputvideo signal into a first sub period and a second sub period, and thedrive voltage applied to the sub periods is different in polarity.

[0115] As described above, in the thirty-fifth aspect, by adjustablybalancing the drive voltage between positive and negative on the basisof vertical scanning period, the echo phenomenon can be restrained.

[0116] A thirty-sixth aspect is directed to an image display method fordisplaying an image by driving a display device based on an input videosignal, comprising

[0117] a drive step of driving the display device by switching a drivevoltage between positive and negative for application based on the inputvideo signal, wherein

[0118] the drive step divides one vertical scanning period of the inputvideo signal into a first sub period and a second sub period, andoutputs the input video signal in the first sub period, and outputs acompensation signal in the second sub period.

[0119] As described above, in the thirty-sixth aspect, irrelevant to theinput video signal, a compensation signal which affects image displaynot that much is inserted to each vertical scanning period. In thismanner, uneven ion distribution is eased, and the echo phenomenon can berestrained.

[0120] A thirty-seventh aspect is directed to an image display methodfor displaying an image by driving a display device based on an inputvideo signal, comprising

[0121] a drive step of driving the display device by switching a drivevoltage between positive and negative for application based on the inputvideo signal, wherein

[0122] the drive step

[0123] scans, in an n-th frame, odd-numbered scanning lines for a datasignal, and even-numbered scanning lines for a compensation signal, and

[0124] scans, in an n+1-th frame, the odd-numbered scanning lines forthe compensation signal, and the even-numbered lines for the datasignal.

[0125] As described above, in the thirty-seventh aspect, by inserting acompensation signal to all of the pixels on a frame basis, uneven iondistribution can be eased, and the echo phenomenon can be suppressed.Further, the timing for displaying the compensation signal may beshifted by one frame depending on whether the scanning line isodd-numbered or even-numbered. This prevents the screen gets blackenedin its entirely for every other frame due to the compensation signal,for example. Moreover, when the video signal is an interlace signal,there is no need to convert it to a progressive signal. Therefore, theimage display apparatus can be realized at relatively low cost.

[0126] A thirty-eighth aspect is directed to an image display method fordisplaying an image by driving a display device based on an input videosignal, comprising

[0127] a drive step of driving the display device by switching a drivevoltage between positive and negative for application based on the inputvideo signal, wherein

[0128] during one vertical scanning period of the input video signal,after sequentially scanning either ones of the odd-numbered scanninglines and the even-numbered scanning lines, the drive step sequentiallyscans the scanning line.

[0129] As described above, in the thirty-eighth aspect, since aperiodical change in brightness being a cause of the echo phenomenon isshifted by a half period for any adjacent scanning lines, the echophenomenon becomes not perceivable.

[0130] A thirty-ninth aspect is directed to an image display method fordisplaying an image by driving a display device based on an input videosignal, comprising

[0131] a drive step of driving the display device by switching a drivevoltage between positive and negative for application based on the inputvideo signal, wherein

[0132] the drive step applies the drive voltage of the same polaritywithout polarity reverse to at least any two successive frames.

[0133] As described above, in the thirty-ninth aspect, the drive voltageis corrected to be in better balance between positive and negative, andthus the echo phenomenon can be restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0134]FIG. 1 is a block diagram showing the structure of a liquidcrystal display apparatus according to a first embodiment of the presentinvention.

[0135]FIG. 2 is a top view of the structure of a liquid crystal panel108.

[0136]FIG. 3 are section views of the structure of the liquid crystalpanel 108.

[0137]FIG. 4 is a diagram showing waveforms of a voltage to be appliedto a pixel.

[0138]FIG. 5 is a diagram showing waveforms of a voltage to be appliedto a pixel.

[0139]FIG. 6 is a block diagram showing the structure of a modificationexample of the first embodiment.

[0140]FIG. 7 is a block diagram showing the structure of a liquidcrystal display apparatus according to a second embodiment of thepresent invention.

[0141]FIG. 8 is a block diagram showing the structure of a double-speedcircuit 112.

[0142]FIG. 9 shows timing charts of the operation of the double-speedcircuit 112.

[0143]FIG. 10 is a diagram showing waveforms of a voltage to be appliedto a pixel.

[0144]FIG. 11 is a block diagram showing the structure of a modificationexample of the second embodiment.

[0145]FIG. 12 is a block diagram showing the structure of a liquidcrystal display apparatus according to a third embodiment of the presentinvention.

[0146]FIG. 13 is a diagram showing the structure of a liquid crystalpanel 132.

[0147]FIG. 14 is a block diagram showing the structure of a liquidcrystal display apparatus according to a fourth embodiment of thepresent invention.

[0148]FIG. 15 is a block diagram showing the structure of a liquidcrystal display apparatus according to a fifth embodiment of the presentinvention.

[0149]FIG. 16 is a diagram showing an exemplary structure of a liquidcrystal panel.

[0150]FIG. 17 is a block diagram showing the structure of a liquidcrystal display apparatus according to a sixth embodiment of the presentinvention.

[0151]FIG. 18 is a diagram showing waveforms of a voltage to be appliedto a pixel.

[0152]FIG. 19 are diagrams showing the relationship between brightnessand voltage in a liquid crystal panel in an NB mode or an NW mode.

[0153]FIG. 20 is a block diagram showing the structure of a liquidcrystal display apparatus according to a seventh embodiment of thepresent invention.

[0154]FIG. 21 is a diagram showing waveforms of a voltage to be appliedto a pixel.

[0155]FIG. 22 is a block diagram showing the structure of a liquidcrystal display apparatus according to an eighth embodiment of thepresent invention.

[0156]FIG. 23 is a diagram showing the change in brightness of any twopixels adjacent to each other.

[0157]FIG. 24 is a block diagram showing the structure of a liquidcrystal display apparatus according to a ninth embodiment of the presentinvention.

[0158]FIG. 25 is a diagram showing waveforms of a voltage to be appliedto a pixel.

[0159]FIG. 26 is a top view of the structure of a liquid crystal panelaccording to a tenth embodiment of the present invention.

[0160]FIG. 27 are section views of the liquid crystal panel of the tenthembodiment.

[0161]FIG. 28 is a diagram illustrating how an echo phenomenon occurs inthe liquid crystal panel 108.

[0162]FIG. 29 is a diagram showing whether the echo phenomenon occursunder what condition.

[0163]FIG. 30 is a diagram showing whether or not the echo phenomenonoccurs in the liquid crystal panel varying in structure according to aneleventh embodiment of the present invention.

[0164]FIG. 31 is a block diagram showing the structure of a conventionalliquid crystal display apparatus.

[0165]FIG. 32 is a diagram showing waveforms of a drive voltage when atest pattern of still images showing gray, white, and gray in thehorizontal direction is displayed under a conventionalAlternating-Current drive method.

[0166]FIG. 33 are diagrams showing the electrode structure of anIPS-type liquid crystal panel.

[0167]FIG. 34 is a diagram showing drive voltage waveforms, in theconventional liquid crystal display apparatus including the IPS-typeliquid crystal panel, in a case where a test pattern of white, gray, andwhite is moved rightward by two pixels on a frame basis.

[0168]FIG. 35 are diagrams showing an electrode voltage of a focusingpixel A shown in FIG. 34, and an electric field relating to the focusingpixel A.

[0169]FIG. 36 is a diagram showing polarization occurred in aninsulation film and uneven distribution of ions in the liquid crystal asa result of DC voltage application in the IPS-type liquid crystal panel,(−) to a common electrode 921, and (+) to a drain electrode 922.

[0170]FIG. 37 is a diagram showing an exemplary image display when atest pattern is moved leftward in the conventional liquid crystaldisplay apparatus.

[0171]FIG. 38 is a diagram for illustrating how echo streaks occur inthe conventional liquid crystal display apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0172] In the below, various embodiments of the present invention aredescribed by referring to the accompanying drawings.

[0173] (First Embodiment)

[0174] In a first embodiment, the above described echo phenomenon isprevented by correcting absolute values of a drive voltage with which aliquid crystal panel is operated under AC drive, whereby the drivevoltage is so adjusted as to balance between positive and negative. FIG.1 shows the structure of a liquid crystal display apparatus of thepresent embodiment. The liquid crystal display apparatus includes anecho suppression circuit 100, a controller 102, a source driver 104, agate driver 106, and a liquid crystal panel 108.

[0175]FIG. 2, and FIG. 3(a) to FIG. 3(c) show the structure of theliquid crystal panel 108. FIG. 2 is a top view of a unit pixel part ofthe liquid crystal panel 108. FIG. 3(a) to FIG. 3(c) show, respectively,a section view along A-A of FIG. 2, a section view along B-B, and asection view along C-C. In the below, by referring to these drawings,the structure of the liquid crystal panel 108 is described. Here, theliquid crystal panel 108 is a general type as an IPS-type liquid crystalpanel.

[0176] On a glass substrate 1, as metal leads, a video signal line(source line) 7 and a scanning signal line (gate line) 4 are placed in amatrix, and at each intersection point thereon, a TFT (Thin FilmTransistor) is formed as a switching element. On the glass substrate 1,a gate electrode 4 and common electrodes 5 and 6 made of metal such asAl are formed simultaneously. In the case where the gate electrode 4 andthe common electrodes 5 and 6 are made of Al, the displaying area isentirely subjected to an anodic oxidation process so as to effectivelyprevent shorts between layers at a part where leads are intersected.Next, a first insulator film 20 (interlayer insulator film) is formed,and then a semiconductor film (amorphous silicon layer) 40 and aprotection layer of the transistor are sequentially formed.

[0177] Then, a contact hole having the first insulator film removedtherefrom is formed in a part not including the display part but beingin the vicinity thereof. And thereby, contact with the lead part to beformed next becomes possible. Next, by using metal such as Al and Ti,the signal lead (source line) 7, a drain line 14, and pixel electrodes 8and 9 are formed. In order to protect thus formed TFT, a secondinsulator film (passivation film) 22 is formed by using SiNx. The secondinsulator film 22 is so formed as to cover a pixel part in its entirety.As to other part except for the display part, the second insulator filmis removed therefrom for such a reason that a terminal part is locatedthere for application of electrical signals.

[0178] The resultant array substrate and a color filter substrate 16 areboth provided with an orientation film 30 so that liquid crystal 3 issandwiched thereby, generating the liquid crystal panel 108. Here, theliquid crystal 3 includes, as does the general IPS-type liquid crystalpanel, a compound including CN group.

[0179] Described below is the operation in the first embodiment. To theliquid crystal display apparatus, a video signal, and ahorizontal/vertical synchronizing signal are to be inputted. The echosuppression circuit 100 corrects the incoming video signal in a manneras will be described later to suppress an echo phenomenon which occurswhen a video signal including moving images is displayed on the liquidcrystal display 108. The controller 102 operates the liquid crystalpanel with AC drive through the source driver 104 and the gate driver106 based on the video signal thus corrected by the echo suppressioncircuit 100, for example.

[0180] Described next is the operation of the echo suppression circuit100. Focusing on one pixel, in the conventional drive method, such avoltage as shown in FIG. 4(a) is applied to the liquid crystal. In thiscase, the voltage to be applied to the liquid crystal is out of balancebetween positive and negative, and therefore the above described echophenomenon occurs in streaks. In the present embodiment, on the otherhand, the video signal is corrected by the echo suppression circuit 100in such a manner as to balance, between positive and negative, thevoltage to be applied to the liquid crystal. Accordingly, as shown inFIG. 4(b), FIG. 4(c), or FIG. 4(d), the voltage which is in balancebetween positive and negative can be applied to the liquid crystal.

[0181] The echo suppression circuit 100 divides the video signal into apair of two successive frames, and for every pair, compares these twoframes in terms of signal level. Then, if these frames are determined asbeing not the same in signal level, the signal is so corrected as to bethe same in signal level between those. At this time, for example, thehigher signal level may be used as a correction basis, or the lowersignal level may be used as the correction basis. Or an average signallevel may be taken between these two frames to use it as the correctionbasis, or any other levels may be used as the correction basis. FIG.4(b) shows the drive voltage to the liquid crystal with the correctionbasis of the lower level, FIG. 4(c) shows the drive voltage to theliquid crystal with the correction basis of the higher level, and FIG.4(d) shows the drive voltage to the liquid crystal with the correctionbasis of the average level.

[0182] As shown in FIG. 4(b) or FIG. 4(c), by using the higher level(maximum) or the lower level (minimum) of the compared frames as a basisof correcting the signal level thereof, contrast between bright and darkis emphasized to a greater degree than the case where the average levelis taken between the frames to use it as the basis as shown in FIG.4(d). Accordingly, there is such an advantage that the time-baserepresentation of videos will become well-defined. On the other hand, byusing the average level of the frames as the basis as shown in FIG.4(d), gradual temporal change in tone can be achieved so that the movingimages can be advantageously displayed more smoothly. Also by using theaverage level of the frames as the basis, a change occurring to the sumof the absolute values of the drive voltage is smaller compared with thecase where no correction is performed. Since human eyes hardly perceivea change in brightness caused by correction in such a manner, there isan advantage that correction can be performed without that muchinfluence.

[0183] Alternatively, correction may be performed always on the basis ofeither the maximum value or the minimum value, or the basis may beswitched therebetween depending on the situation. In the case wherecorrection is performed always on the basis of either the maximum valueor the minimum value, the circuit structure can be advantageouslysimplified. Alternatively, as an example, a reference intermediate tonelevel (e.g., a value which is exactly in the middle between the maximumtone level and the minimum tone level of the display apparatus) may beprovided. According to the level of the video signal, correction may beperformed based on either the maximum value or the minimum valuewhichever farther from this reference intermediate tone level. Throughsuch correction, the resultant signal turns out to be brighter or darkerthan the intermediate tone so that videos are advantageouslywell-defined easily.

[0184] Here, in the present embodiment, the drive voltage level is firstcompared for every two frames, and then the video signal is so correctedas to equalize the signal level between those two frames. This is notrestrictive, and the number of frames used as the basis of correctingthe video signal to balance the drive voltage level between positive andnegative may be three or four. To be specific, alternatively to theconventional drive method shown in FIG. 5(a), the video signal may becorrected on the basis of three frames as shown in FIG. 5(b) to balancethe drive voltage level between positive and negative. By increasing thenumber of frames to be compared as such, adjustment for incoming videosignals can be done more flexibly compared with the case whereadjustably balancing between positive and negative for every two framesas in the present embodiment, and thus there is an advantage thatcorrection can be performed without that much influence. Assuming herethat the drive voltage is adjustably balanced between positive andnegative on a frame basis of three or more frames. If balance adjustmentbetween positive and negative is done by not correcting any frame signalat least maximum or minimum in signal level among a plurality of framesto be used as the basis but by using any other frame signal, any imagecharacteristic point (e.g., conspicuously bright part or dark part) isprevented from being lost or becoming inconspicuous as a result ofcorrection. Therefore, image degradation due to correction can besuppressed. Further, through such correction as not changing the sum ofthe absolute values of the drive voltage on the basis of frames,correction can be so performed, without that much influence, as not tomake a change in brightness caused thereby perceivable that much.

[0185] Here, the brightness of the liquid crystal display element isproportional to about the square of the drive voltage. In the displayapparatus, generally, the relationship between a tone signal and thebrightness is also proportional to about the square. Accordingly, toperform correction in a manner not to change the sum of the absolutevalues of the brightness with more accuracy, correction may be soperformed as not to change the sum of the square of the drive voltage.If this is the case, correction can be so performed, without that muchinfluence, as to make a change in brightness caused therebyunperceivable. Note here that, retaining the sum of the absolute valuesas mentioned in the above is easier for realization with circuits, forexample.

[0186] Here, those various correction methods described in the above maybe changed as appropriate depending on the situation. For example, thosecorrection methods exemplified by FIG. 4(b), FIG. 4(c), and FIG. 4(d)maybe all used for correction by switching thereamong depending on whatthe video scenes are for.

[0187] Note here that, although many of the correction methods areexemplified in the above, what important to suppress the echo phenomenonis performing correction in a manner that the drive voltage can bebalanced better between positive and negative. In consideration thereof,any other arbitrary correction methods which can achieve that are surelyapplicable also. Moreover, the video signal is subjected to correctionto balance the drive voltage between positive and negative in thepresent embodiment. This is not the only possibility, and the drivevoltage to be outputted from the controller 102 may be subjected tocorrection.

[0188] In order to operate as such, although not shown, the echosuppression circuit 100 needs to include a memory for storing videosignals of a plurality of fields, a computation part for comparing thesignal level among those fields, and a circuit for controlling those. Asto its circuit structure, however, there is no specific limitation,preferably a low-priced simple circuit.

[0189] Further, in the present embodiment, as shown in FIG. 1, the echosuppression circuit 100 is structured separately from otherconstituents, but this is not restrictive. As shown in FIG. 6, forexample, the echo suppression circuit 100 may be functionallyincorporated, in terms of process, into a TV-LCD conversion circuit forinputting TV signals into the liquid crystal panel, or a pixelconversion circuit 110 for resolution conversion, for example. If thisis the case, the number of constituents required for the liquid crystaldisplay apparatus can be reduced, and thus the liquid crystal displayapparatus can be realized at relatively low cost.

[0190] Still further, in the present embodiment, correction is performedfor every pair of two frames in such a manner as to equalize theabsolute values of the drive voltage. This is not restrictive, andbringing the absolute values closer to each other as much as possiblecan also reduce the echo phenomenon. Specifically, the echo phenomenonprovably shows considerable improvement when correction is so performedas to keep a difference of absolute values a half of the maximum drivevoltage or smaller. Furthermore, when correction is so performed as tokeep the difference of absolute values smaller than a tenth thereof, theecho phenomenon is successfully suppressed to a level unobservable bythe naked eyes. These results show that, limitedly performing correctiononly when any two successive frames show a difference of absolute valuesof the drive voltage being a tenth of the maximum drive voltage orlarger will lead to more efficiency at the time of correction.

[0191] Still further, in the present embodiment, correction is soperformed as to balance the drive voltage between positive and negativeon the basis of a plurality of frames. This is not restrictive, and forexample, correction may be performed sequentially through framecomparison, one frame with another frame precedent thereto. If this isthe case, with respect to any frame to be corrected, considering notonly a frame precedent thereto but also another frame subsequent theretomay give more flexibility to the amount of frame correction to bedetermined.

[0192] As described in the foregoing, according to the first embodiment,by correcting video signals composed of frames or a drive voltage on thebasis of a plurality of frames in such a manner as to balance, betweenpositive and negative, the drive voltage to liquid crystal, an echophenomenon can be prevented when moving images are displayed.

[0193] (Second Embodiment)

[0194] In a second embodiment, the above described echo phenomenon isprevented by alternating the polarity of a drive voltage with which aliquid crystal panel is driven, whereby the drive voltage is so adjustedas to balance between positive and negative for each frame. FIG. 7 showsthe structure of a liquid crystal display apparatus according to thesecond embodiment of the present invention. In FIG. 7, the liquidcrystal display apparatus includes a double-speed circuit 112, thecontroller 102, the source driver 104, the gate driver 106, and theliquid crystal panel 108. In the below, the operation in the presentembodiment is described.

[0195] The double-speed circuit 112 converts, based on incoming videosignal and synchronizing signal to be inputted, a frame frequency of theincoming video signal to be doubled. The controller 102 performs timingcontrol of the source driver 104 and the gate driver 106, and AD drivecontrol of the liquid crystal panel 108 based on an output from thedouble-speed circuit 112. In the below, the structure and the operationof the double-speed circuit 112 is described in more detail.

[0196]FIG. 8 is a block diagram showing an exemplary structure of thedouble-speed circuit 112 of the present embodiment. In FIG. 8, thedouble-speed circuit 112 includes a dual port RAM 114, a writing addresscontrol circuit 116, a reading address control circuit 118, and asynchronizing signal control circuit 120.

[0197] The dual port RAM 114 is a random access memory in which awriting address/data port and a reading address/data port are providedseparately, and accordingly writing and reading can be performedseparately. An incoming video signal is inputted into the writing portof the dual port RAM 114, and according to a writing address coming fromthe writing address control circuit 116, written into the dual port RAM114. The video signal data thus written into the dual port RAM 114 isthen read and outputted by the dual port RAM 114 in accordance with areading address coming from the reading address control circuit 118. Inresponse to an input vertical synchronizing signal, an input horizontalsynchronizing signal, and an input clock, the synchronizing signalcontrol circuit 120 controls both the writing address control circuit116 and the reading address control circuit 118, and also outputs anoutput vertical synchronizing signal, an output horizontal synchronizingsignal, and an output clock which are all converted in frequency to bedoubled with respect to the inputs. In the below, by referring to FIG.9, the operation of the double-speed circuit 112 is described morespecifically.

[0198]FIG. 9 are timing charts showing the operation of the double-speedcircuit 112 of the present embodiment. In FIG. 9, the lateral axisindicates time, and in the vertical direction, indicated for theinput/output vertical synchronizing signals is a signal size, and forthe writing/reading addresses is an address. As shown in FIG. 9, thewriting address outputted from the writing address control circuit 116is counted up responding to a clock input, and reset to a verticalblanking interval responding to the input vertical synchronizing signal.The writing data is an input video signal, and a frame of the inputvideo signal is stored on the dual port RAM 114. The reading address is,on the other hand, counted up responding to an output clock which is theone obtained by multiplying the input clock by a PLL, for example, andreset by a frequency which is the two-fold of the frequency of the inputvertical synchronizing signal. If the timing of resetting the count ofthe reading address is synchronized with the timing of resetting thecount of the writing address, and if the count reset timing of thereading address is coincided with the count reset timing of the writingaddress once to twice, any images showing discontinuity caused bywriting and reading getting out of order can be removed to the outsideof the effective screen. As such, realized is the double-speed circuit112 from which one frame of the input video signal is outputted at thedoubled frame frequency twice in a row.

[0199]FIG. 10(a) is a diagram showing a change occurring to the drivevoltage to the liquid crystal of a focusing pixel when the liquidcrystal is driven under the conventional drive method. FIG. 10(b) is, onthe other hand, a diagram showing a change occurring to the drivevoltage to the liquid crystal of the focusing pixel when the liquidcrystal is driven under the drive method of the present embodiment. Asshown in FIG. 10(b), in the present embodiment, the drive voltage to theliquid crystal is balanced between positive and negative on a framebasis. That is, the polarity of an electric field applied to the liquidcrystal of the pixel A is in balance between positive and negative evenduring pattern passing and thereafter. Therefore, the problem of unevenion distribution in the liquid crystal panel can be prevented in aperiod for vertical scanning the video signal which is originallyinputted. As a result, there occurs no tail echo when displaying movingimages, which is the problem occurring in the conventional liquidcrystal display apparatus.

[0200] As such, according to the present embodiment, the incoming videosignal is so converted as to be doubled in frame frequency for operatingthe liquid crystal panel with AC drive. In detail, each frame of theoriginal video signal is further divided into two periods (sub frames)of a normal period and a compensation period, the length of which is thesame. The polarity is changed between the normal period and thecompensation period for driving the liquid crystal panel, canceling outthe progress of uneven distribution of the ions for each frame of thevideo signal. In such a manner, no matter in what pattern the displayingmoving images are, the ions will never be distributed unevenly to afurther extent, and the insulator film will never be polarized to afurther extent. Accordingly, image degradation as a result of the echophenomenon can be restrained.

[0201] Here, in the above, the liquid crystal panel is presumably theIPS-type liquid crystal panel. This is not the only option, and whateverarbitrary liquid crystal panel in which the echo phenomenon is observedcan surely restrain image degradation as a result of the echophenomenon.

[0202] Further, in the above, the double-speed circuit 112 is structuredby the dual port RAM 114. It can be also realized by using single portRAM to share writing and reading by time. Moreover, the double-speedcircuit 112 is not limited in structure as such, and any other arbitrarystructure is surely applicable thereto. In terms of simplicity and lowcost, the above described structure is considered preferable.

[0203] Note that, in the present embodiment, the original video signalis simply doubled in frame frequency for operation with the verticalscanning period divided into the normal period and the compensationperiod being the same in length. This is not restrictive, and the ratiobetween the normal period and the compensation period may be arbitrary.Here, if the normal period and the compensation period are set the samein length, the signal needs only to be simply doubled so that thecircuit structure is simplified. It should be noted here that somecombination of the panel structure, the liquid crystal material, and theorientation film, for example, may vary ion behavior depending onwhether the frame is driven by the positive drive voltage or negative.Therefore, it is preferable that the length ratio between those two subframes is optimally set in consideration of the ion behavior.

[0204] Here, in the present embodiment, the drive voltage issequentially switched between positive and negative in order dependingon the frame is in the normal period or in the compensation period, andthis switching order is not restrictive. For example, it is so set thatthe normal period of the n-th frame is driven by the positive voltageand the compensation period thereof by the negative voltage, and thenormal period of the n+1-th frame is driven by the negative voltage andthe compensation period thereof by the positive voltage. If this is thecase, the compensation period of the n-th frame and the normal period ofthe n+1-th frame become the same in polarity of the drive voltage.Therefore, the compensation voltage of the preceding frame will haveprecharge effects so that the voltage step at the time of writing thedrive voltage of the normal period. As a result, the required level ofthe charge capacity of the TFT can be advantageously lowered.

[0205] Note that, in the present embodiment, in the double-speed circuit112, signals are doubled in speed by using a memory which is providedfor storing video signals. This is not restrictive, and speed-doublingmay be carried out by using a delay circuit, for example. With the delaycircuit used, the double-speed circuit 112 can be manufactured at lowercost since the memory is not burdened, but at higher speed, thereliability of signals is decreased.

[0206] Further, in the present embodiment, the proprietary circuit isused for speed-doubling. As shown in FIG. 11, for example, thedouble-speed circuit 112 may be functionally incorporated into a TV-LCDconversion circuit for inputting TV signals into the liquid crystalpanel, or a pixel conversion circuit 122 for resolution conversion, forexample. If this is the case, the number of required constituents can bereduced, and thus the liquid crystal display apparatus can be realizedat relatively low cost.

[0207] As described in the foregoing, in the second embodiment, eachvideo signal is divided into two sub frames for driving the liquidcrystal. Thus, signal application to one pixel in one frame needs to bedone twice, making pixel design difficult in the liquid crystal displayapparatus of a higher resolution (XGA or higher). To deal with thisproblem, as a method of enabling high-speed scanning in such a liquidcrystal display apparatus, there is a method of doubling a time takenfor selecting one scanning line, and driving the device in such a mannerthat a half of the time for selecting one scanning line is superposed ona time for selecting the next scanning line, or a method of graduallychanging the capacity Cst, Cgd, or the like, on a pixel basis, forexample. However, even under these techniques, designing the TFT, forexample, becomes more difficult as the resolution gets higher.

[0208] Therefore, shown in a third embodiment is such a structure aseasily enabling the high speed scanning in the liquid crystal displayapparatus.

[0209] (Third Embodiment)

[0210]FIG. 12 shows the structure of a liquid crystal display apparatusof the third embodiment of the present embodiment. Here, in FIG. 12, anyconstituent identical to that of FIG. 11 is provided with the samereference numeral, and not described again. A controller 124 controls afirst source driver 126, a second source driver 128, and a gate driver130. FIG. 13 shows the TFT arrangement of a liquid crystal panel 132. Inthe present embodiment, as shown in FIG. 13, the number of data signallines is doubled, and pixels for two lines are to be driven by onescanning line. And thereby, the time taken for scanning one scanningline can be doubled. In other words, the number of the scanning linescan be reduced to half without lowering the resolution in the verticaldirection. Therefore, even with double-speed drive, the time taken forscanning one scanning line can remain the same as conventional. Here,since the number of the source lines is doubled, wiring density isincreased in the part where the source driver is incorporated. To avoidthis, the source driver may be divided into two, and provided at twopositions as shown in FIG. 13.

[0211] (Fourth Embodiment)

[0212]FIG. 14 shows the structure of a liquid crystal display apparatusaccording to a fourth embodiment of the present invention. Here, in FIG.14, any constituent identical to that of FIG. 11 is provided with thesame reference numeral, and not described again. This liquid crystaldisplay apparatus performs display by switching between a TV videosignal and a PC video signal using a switching switch 134. Specifically,the TV video signal is doubled in speed at the same time as beingconverted into an LCD video signal in the TV-LCD conversioncircuit/pixel conversion circuit 122. On the other hand, the PC videosignal is not doubled in speed when converted into the LCD video signalin a PC-LCD conversion circuit/pixel conversion circuit 136.

[0213] When outputted is the PC signal, displayed is a video with lowerdegree of movement, and thus no echo phenomenon is observed.Accordingly, in the present embodiment, as shown in FIG. 14, whendisplaying moving images such as TV/VTR signals, speed-doubling iscarried out as in the above described second embodiment, and the liquidcrystal is driven through polarity reverse after dividing each videosignal into two sub frames. When displaying the PC signal, on the otherhand, in a manner similar to the conventional, the polarity of the datasignal is reversed on a frame basis for driving.

[0214] As such, according to the fourth embodiment, realized is theliquid crystal display apparatus in which no echo phenomenon is observedwhen displaying moving images such as TV/VTR signals. Note that, thecurrent TV/VTR signals are interlace signals, and thus the resolution inthe direction of vertical scanning is ½. Thus, in order to display suchTV/VTR signals, there requires an interlace-progressive (IP) conversioncircuit in the TV-LCD conversion circuit/pixel conversion circuit 122.Accordingly, in the present embodiment, any signal processing relatingto the TV video signals is realized in one circuit, reducing the numberof constituents and cost. In this view, the present embodiment isconsidered suitable for a case where video signals of moving images areinterlace signals.

[0215] (Fifth Embodiment)

[0216]FIG. 15 shows the structure of a liquid crystal display apparatusaccording to a fifth embodiment of the present invention. Here, in FIG.15, any constituent identical to that of FIG. 14 is provided with thesame reference numeral, and not described again. This liquid crystaldisplay apparatus performs display by switching between the TV videosignal and the PC video signal using the switching switch 134.

[0217] When outputted is the PC signal, displayed is a video with lowerdegree of movement, and thus no echo phenomenon is observed.Accordingly, in the present embodiment, as shown in FIG. 15, whendisplaying moving images such as TV/VTR signals, speed-doubling iscarried out as in the above described second embodiment, and the liquidcrystal is driven through polarity reverse after dividing each videosignal into two sub frames. If this is the case, a controller 137controls the gate driver 106 in such a manner as to scan two scanningline at one time. With such a structure, those two scanning lines whichare scanned at the same time is written with the same signal. Therefore,the resolution in the direction of the scanning line reduced to ½, whilethe charge time for one scanning line can remain the same asconventional for scanning. Here, as shown in FIG. 16, also by placingTFTs in a staggered arrangement with respect to the gate wiring, thefact that the resolution in the direction of the scanning line has beendropped to ½ can be hardly perceived by the naked eyes. When displayingthe PC signal, on the other hand, in a manner similar to theconventional, the polarity of the data signal is reversed on a framebasis for driving.

[0218] As such, according to the fifth embodiment, with the conventionalTFT capacity, the PC signal can be displayed without lowering theresolution. Also, when displaying moving images such as TV/VTR signals,realized is the liquid crystal display apparatus in which no echophenomenon is observed. Here, since the current TV/VTR signals areinterlace signals, the resolution in the direction of the verticalscanning lines is ½. Therefore, there requires no interlace-progressive(IP) conversion circuit in the liquid crystal display apparatus of thepresent invention, successfully lowering the cost. Thus, the presentinvention is considered suitable for a case where video signals ofmoving images are interlace signals.

[0219] (Sixth Embodiment)

[0220]FIG. 17 shows the structure of a liquid crystal display apparatusaccording to a sixth embodiment of the present invention. Here, in FIG.17, any constituent identical to that of FIG. 1 is provided with thesame reference numeral, and not described again. In the presentembodiment, in an echo suppression circuit 138, for the purpose ofeasing uneven ion distribution, the video signal is corrected in such amanner as to insert thereto a compensation signal of a black-levelvoltage which hardly affects displaying videos. In the below, anexemplary case of using a panel of NB mode is described in a specificmanner.

[0221]FIG. 18(a) shows an example of voltage application to one pixelunder the conventional drive method. Also, FIG. 18(b) shows anotherexample of voltage application to one pixel under a drive method of thepresent embodiment. Under the conventional drive method, the videosignal is applied to each frame for the duration of a frame. But underthe drive method of the present embodiment, each frame is divided intotwo sub frames of a first sub frame and a second sub frame. And in thefirst sub frame, a video signal is applied, and applied in the secondsub frame is a black video signal, i.e., the drive voltage of 0V as acompensation signal for canceling uneven ion distribution. Then, on thebasis of a frame (on the basis of two sub frames), the polarity of thevoltage applied to the liquid crystal is reversed. Here, the lengthratio between the first sub frame and the second sub frame is notnecessarily be 1:1. The longer the length of the second sub frame, thedarker the display screen becomes. Therefore, as to this length, theshorter would be the better.

[0222] In the present embodiment, through such operation, uneven iondistribution occurred as a result of application of the drive voltage inthe first sub frame can be eased by application of the black-levelvoltage in the second sub frame. Accordingly, uneven ion distribution iseased in each frame, resultantly suppressing the occurrence of the echophenomenon.

[0223] In the present embodiment, the display period for the videosignal becomes shorter than one frame. Generally, the conventionalliquid crystal display apparatus has been a hold-type display device,and as a common notion, moving images are considered easily blurredtherein compared in a pulse-type display device such as CRTs (ElectricalCommunications Association papers vol. 1. J68B, No. 12 (1985-12)). Underthe drive method of the present embodiment, since each frame isblackened for once as already described, there is an advantage that blurinherent in the hold-type display device hardly occurs.

[0224] Here, in the present embodiment, similarly to the secondembodiment, signal application needs to be done twice to a single pixelon a frame basis. Accordingly, the drive methods in the third embodimentand the fourth embodiment may be combined for further effects.

[0225] Note that, in the present embodiment, the black-level voltageapplied to the second sub frame is assumed to be 0V. Actually, however,the black-level voltage is often not 0V due to the manufacturing reasonsof the liquid crystal display apparatus. In such a case, as exemplaryvoltage application to one pixel, there may be two manners as shown inFIG. 18(c) and FIG. 18(d). FIG. 18(c) shows a case where the first subframe and the second sub frame are the same in polarity, while FIG.18(d) shows a case where the first sub frame and the second sub frameare not the same in polarity. Here, the black-level voltage at this timeis preferably of a pedestal level or lower. Further, to the second subframe, applying the black level different in polarity from that to thefirst sub frame as shown in FIG. 18(d) is better than applying the blacklevel the same in polarity from that to the first sub frame as shown inFIG. 18(c). This is because, thereby, uneven ion distribution is easilyeased, and thus it is considered preferable in view of suppressing theecho phenomenon.

[0226] Here, the voltage of pedestrian level or lower means the voltageshowing an absolute value farther from white than the original blacksignal. By taking a liquid crystal display apparatus in NB mode as anexample, the relationship of T-V property (brightness-voltage property)will be such a relationship as shown in FIG. 19(a). A voltage AA shownin FIG. 19(a) is the voltage at the time of displaying a black signalbased on the video signal in the normal manner. In the liquid crystaldisplay apparatus in NB mode, the voltage of the pedestal level or lowermeans the voltage equal to or lower than the voltage AA. By using thevoltage lower than the pedestal level as a compensation signal, thechange observed in absolute values between the video signal and thecompensation signal becomes larger than the case where the generalblack-level voltage (voltage AA) is used. As a result, uneven iondistribution is cancelled much faster, and accordingly the echophenomenon can be suppressed more effectively. Here, in the case of aliquid crystal display apparatus in NW mode, the relationship of T-Vproperty will be such a relationship as shown in FIG. 9(b). Accordingly,to achieve the same effects as the case of NB mode described in theabove, as a compensation signal, the voltage equal to or higher than thepedestal level, that is, the voltage equal to or higher than the generalblack-level voltage (voltage BB) may be used.

[0227] Further, in the present embodiment, there needs to write thesignal voltage to each pixel on the basis of a scanning line in thefirst sub frame, but in the second sub frame, written into each pixel isthe same compensation voltage. Thus, n lines (e.g., four lines) may bewritten with the compensation signal all at once. If so, the writingperiod of the second sub frame can be reduced to 1/n compared with thewriting period of the first sub frame. As a result, the charge time fora scanning line to which the signal voltage is written can be longer,and thus demands for the charging property of the TFT can be eased.

[0228] (Seventh Embodiment)

[0229]FIG. 20 shows the structure of a liquid crystal display apparatusaccording to a seventh embodiment of the present embodiment. Here, inFIG. 20, any constituent identical to that of FIG. 1 is provided withthe same reference numeral, and not described again. In the presentembodiment, similarly to the sixth embodiment in the above, in an echosuppression circuit 140, a video signal is so corrected as to beinserted with a compensation signal of a black-level voltage whichhardly affects displaying videos for the purpose of easing uneven iondistribution. In the below, an exemplary case of using a panel in NBmode is described specifically.

[0230]FIG. 21(a) shows exemplary voltage application to a pixel underthe conventional drive method. And FIG. 21(b) shows another exemplaryvoltage application to a pixel under a drive method of the presentembodiment. Here, in the above described sixth embodiment, since signalapplication has to be done twice for a pixel in each frame, TFTs in thepixels and peripheral circuits may be limited in design. In the presentembodiment, on the other hand, applied to a pixel in the first frame isa signal voltage, and to the second frame is a black video signal, i.e.,a drive voltage of 0V, as a compensation signal for canceling uneven iondistribution. Thereafter, the polarity of the signal voltage is reversedfor every two frames.

[0231] In the present embodiment, through such operation, uneven iondistribution occurred as a result of application of the drive voltage inthe first frame can be cancelled by application of the black-levelvoltage in the second frame. Accordingly, uneven ion distribution iscancelled in two frames, resultantly suppressing the occurrence of theecho phenomenon.

[0232] Here, if the black voltage is applied to all of the pixels on thedisplay screen at the same time, flicker occurs at a frequency half ofthat of the video signal. Thus, in order to prevent this, frame shiftingis taken place in a one-to-one relationship to lines, columns, or dots.Assuming here that the video signal is applied to even-numbered lines inan n-th frame, and the black-level signal is applied to odd-numberedlines therein. Then, in an n+1-th frame, applied to odd-numbered linesis the video signal, and the black-level signal is applied toeven-numbered lines. If this is the case, the resolution in one frame ofthe screen is actually reduced to half, but because of the human eyes'accumulated effects, the resolution will be reduced only about 25%.Presently, since video signal used for TVs and VTRs are often in theinterlace format, with drive of the present invention in accordance withthe respective format of the video signals, there requires nointerlace-progressive (IP) conversion circuit, reducing the cost of theresultant liquid crystal display apparatus. In this view, the presentembodiment is considered suitable for a case where input video signalsare interlace signals.

[0233] (Eighth Embodiment)

[0234]FIG. 22 shows the structure of a liquid crystal display apparatusaccording to an eighth embodiment of the present invention. Here, inFIG. 22, any constituent identical to that of FIG. 1 is provided withthe same reference numeral, and not described again. In the conventionalliquid crystal display apparatus, the scanning lines have beensequentially scanned in order line by line. Conversely, in the presentembodiment, the scanning lines are scanned every other line by acontroller 142.

[0235]FIG. 23(a) and FIG. 23(b) show a change in brightness observed in,respectively, any two pixels adjacent to each other in response to anyDirect-Current component applied thereto. From FIG. 23(a) and FIG. 23(b)showing changes in brightness, it is known that the brightness starts toperiodically vary after the DC voltage application, and the echophenomenon is observed in both of those pixels.

[0236] However, under the drive method of the present embodiment, asshown in FIG. 23(a) and FIG. 23(b), the drive voltage waveform of theliquid crystal of those adjacent pixels is shifted by a half period.When a person sees such two pixels, his/her eyes may spatially averagethose, and recognize that as a change in brightness as shown in FIG.23(c). Therefore, no echo phenomenon is to be observed.

[0237] (Ninth Embodiment)

[0238]FIG. 24 shows the structure of a liquid crystal display apparatusaccording to a ninth embodiment of the present invention. Here, in FIG.24, any constituent identical to that of FIG. 1 is provided with thesame reference numeral, and not described again. In the conventionalliquid crystal display apparatus, the polarity of the drive voltage isso set as to alternate frame by frame. In the present embodiment, on theother hand, for the purpose of restraining the echo phenomenon, acontroller 144 controls the drive voltage in such a manner that thepolarity does not alternate once for n frames. Here, n is presumably 2or larger.

[0239]FIG. 25(a) is a diagram showing a change observed in the drivevoltage applied to the liquid crystal of a focusing pixel in a casewhere the liquid crystal is driven under the conventional drive method.FIG. 25(b) is a diagram showing a change observed in the drive voltageof the liquid crystal of the focusing pixel in a case where the polarityof the drive voltage is not alternated once for every two frames. AndFIG. 25(c) is a diagram showing a change observed in the drive voltageapplied to the liquid crystal of the focusing pixel in a case where thepolarity of the drive voltage is not alternated once for every 9 frames.

[0240] As such, by setting the polarity of the drive voltage not toalternate once for n frames, it is confirmed that the echo phenomenoncan be successfully restrained. This is because, with the conventionalAC drive as shown in FIG. 25(a), the ratio between a positive part and anegative part both diagonally shaded therein is about 2:1, and when thepolarity alternates for every two frames as shown in FIG. 25(b), theratio between a positive part and a negative part both diagonally shadedtherein is about 3:2. In view of the comparison result derived by thoseshaded parts, the latter is considered better balanced. Further, asshown in FIG. 25(c), the echo phenomenon is confirmed as beingrestrained also when the polarity is so set as not to alternate once fornine frames. In this case, if any one of the nine frames except forthose shaded in FIG. 25(c) is conspicuously high in voltage as the 5thframe shown in FIG. 25(a), an echo phenomenon occurs due to the voltageof higher level but is definitely restrained compared with the caseunder the conventional AC drive. If such a voltage of higher level isfound in the shaded frame(s) shown in FIG. 25(c), however, an echophenomenon is problematically encouraged to occur compared with the caseunder the conventional AC drive. As shown in FIG. 25(c), however, theshaded parts occupy no more than {fraction (2/9)} as a whole. Therefore,even if an input signal pattern shows one frame conspicuously high involtage, the probability of the voltage of the higher level applying tothose shaded parts, that is, the successive frames of the same polarityis merely {fraction (2/9)}. Accordingly, in terms of the probabilitytheory, an echo phenomenon is successfully suppressed. Here, in FIG.25(c), the polarity of the drive voltage does not alternate once fornine frames, but this is not restrictive.

[0241] As described in the above, according to the ninth embodiment,there only needs to change the timing for polarity reverse of the drivevoltage. Accordingly, the echo phenomenon can be suppressed quiteeasily.

[0242] (Tenth Embodiment)

[0243]FIG. 26 shows a top view of a unit pixel of a liquid crystal panelaccording to a tenth embodiment of the present invention. In the presentembodiment, in order to ease uneven ion distribution, a pixel electrodeand a common electrode apply the voltage to the liquid crystal onlythrough an orientation film. FIG. 27(a) is a section view along B-Bshown in FIG. 26. FIG. 27(b) is a section view along B-B shown in FIG.26. With such a structure, according to the present embodiment, iondistribution in the liquid crystal will not become so uneven comparedwith the general IPS-type liquid crystal panel shown in FIG. 2 and FIG.3. In the below, a further description is given. It should be noted herethat the structures shown in FIG. 26 and FIG. 27 are not more than aspecific example, and not restrictive.

[0244] On the glass substrate 1 which is a part of the liquid crystalpanel, as metal leads, the video signal line (source line) 7 and thescanning signal line (gate line) 4 are placed in a matrix. At eachintersection point of these signal lines, a TFT (Thin Film Transistor)15 is formed as a switching element. On the glass substrate 1, the gateelectrode 4 and the common electrodes 5 and 6 made of metal such as Alare formed simultaneously. Next, the first insulator film 20 (interlayerinsulator film) is formed, and then a semiconductor film (amorphoussilicon layer) and a protection layer of the transistor are sequentiallyformed. Then, the first insulator film 20 is removed from a part notincluding the display part but being in the vicinity thereof so thatcontact with the lead part becomes possible. And at the same time, thefirst insulator film 20 on the common electrode in the pixel ispartially removed, and thus a contact hole is formed.

[0245] Then, by using metal such as Al/Ti, formed are another signallead (source line) 7, the drain line 14, the pixel electrodes 8 and 9,and a second common electrode 12. At this time, the second commonelectrode 12 is electrically connected to the first common electrode 5via the contact hole 10. Here, the first common electrode 5, the secondcommon electrode 12, and the contact hole 10 are not specificallylimited in placement position. Here, by placing the first commonelectrode farther from the gate wiring, shorts between the gate wiringand the common electrodes can be prevented.

[0246] In order to protect thus formed TFT on the substrate, SiNx isformed as the second insulator film (passivation film) 22. The secondinsulator film 22 on a terminal part by which an electrical signal forthe part around the display area but not including the same is appliedis removed, and the second insulator film 22 is also removed from therest of the part excluding the TFTs in the pixel.

[0247] With such a structure, in the present embodiment, no echophenomenon occurs when displaying moving images. As shown in FIG. 27(a)and FIG. 27(b), inorganic insulator films over the pixel electrodes andthe common electrodes have been removed, and thus the pixel electrodesand the common electrodes apply the voltage to the liquid crystal viaonly the orientation film. Therefore, even if ions get distributedunevenly, thus unevenly distributed ions become nonionic as arerecovered by the pixel electrodes and the common electrodes.

[0248] Note that, in the present embodiment, both of the pixel electrodeand the common electrode are abutting to the liquid crystal only throughthe orientation film, but this is not restrictive. If at least a part ofthe pixel electrode and the common electrode is so structured as toapply the voltage to the above described liquid crystal only through theabove described orientation film, uneven ion distribution is accordinglyeased and the echo phenomenon is suppressed. That is, such a structurewill do as, in the unit pixel, as at least a part of the pixel electrodeand the common electrode are so structured as to apply the voltage tothe liquid crystal only through the orientation film.

[0249] (Eleventh Embodiment)

[0250] As an eleventh embodiment of the present invention, described isthe structure of a liquid crystal panel in which ions hardly getunevenly distributed.

[0251] For reference purpose, FIG. 28(a) and FIG. 28(b) show a change inbrightness when a Direct-Current component is applied to a pixel of thegeneral IPS-type liquid crystal panel 108 shown in FIG. 2, and FIG. 3(a)to FIG. 3(c). FIG. 28(a) shows a voltage level to be applied to thepixel, and FIG. 28(b) shows a change in brightness when a voltageapplied thereto is of the voltage level. In the liquid crystal panel108, the brightness periodically varies as shown in FIG. 28(b), and as aresult, an echo phenomenon is observed.

[0252] Here, as to the material structuring the liquid crystal panel, asshown in FIG. 29, the echo phenomenon is found as observed in any of aliquid crystal panel using liquid crystal which includes 1% or more of aCN compound, a liquid crystal panel using a polyimide orientation film(low-resistance orientation film) which includes the following compoundwhose conjugated length is seven or more atoms, a liquid crystal panelusing liquid crystal to which such an additive as ionic compound isadded, and a liquid crystal panel in which the volume of ions in liquidcrystal is increased by irradiating UV ray to the liquid crystal, forexample.

[0253] Herein, an IPS-system is exemplified for comparison purpose, butany other liquid crystal modes may lead to the same phenomenon. Also,this array substrate structure is not restrictive, and this structure isno more than an exemplary one for comparison.

[0254] The liquid crystal panel of the present embodiment is the same asthe liquid crystal panel 108 shown in FIG. 2 and others except for theliquid crystal and the orientation film material. The liquid crystalused in the present embodiment is the one including no CN compound, andthe orientation film is a polyimide high-resistance orientation filmincluding no such compound as having the conjugated length of seven ormore atoms, but including the following compound.

[0255] By taking liquid crystal panels each manufactured by arbitrarilycombining liquid crystal A to B varying in type, and orientation films Ato C all satisfying such conditions, as shown in FIG. 30, a voltageholding ratio at 40 degrees is 98% or more, and the ion density will be1×10⁻¹³ cm⁻³ or lower, proving that no echo phenomenon occurs whenmoving images are displayed.

[0256] As such, according to the liquid crystal panel of the presentembodiment, the material to be used therefor has the smaller number ofimpurity ions in the liquid crystal and the orientation film, and highin resistance. Therefore, no echo phenomenon occurs.

[0257] Here, even if no echo phenomenon occurs, due to slow responsespeed, a tail phenomenon inconveniently occurs when displaying movingimages. Accordingly, in view of the response speed, described below isthe guideline for property constants of the liquid crystal material.

[0258] The following equation (1) is an equation relating to theresponse speed (τr) at a rising edge, equation (2) is an equationrelating to the speed (τd) of a falling edge, and equation (3) is anequation relating to the voltage of the rising edge. $\begin{matrix}{\tau_{r} = \frac{\gamma}{{{ɛ0} \times {\Delta_{ɛ}\left( {V/L} \right)}^{2}} - {K\quad {\pi^{2}/d^{2}}}}} & (1) \\{\tau_{d} = \frac{\gamma \quad d^{2}}{K\quad \pi^{2}}} & (2) \\{{V\quad t\quad h} = {\frac{\pi \quad 1}{d}\sqrt{\frac{K}{{ɛ0} \times \Delta_{ɛ}}}}} & (3)\end{matrix}$

[0259] Here, in the equation (1), the equation (2), and the equation(3), γ denotes a rotational viscosity, K denotes an elastic constant, Idenotes a space between electrodes, V denotes a voltage, and d denotes agap.

[0260] The response speed is preferably 1 ms or smaller, and practicallyit is 40 ms or smaller since τr+τd, and preferably it is 30 ms orsmaller. As is evident from the equation (1) and the equation (2), thesmaller γ will increase the response speed. The problem is that reducingγ without using the liquid crystal including CN group is considerablydifficult under present circumstances. Thus, instead, try to reduce d toincrease the response speed. In order to reduce d, there needs toincrease Δn. If the drive voltage between the pixel electrode and thecommon electrode has any allowance, Δε may be small in value.Accordingly, the guideline for designing the liquid crystal material isto set Δn as large as possible, and γ as small as possible within arange not affecting the characteristics (especially reliability) of theliquid crystal display apparatus.

[0261] To be specific, γ preferably takes a value in the range of 100 to140 mPa·s (preferably 120 or smaller, but 130 to 140 under presentcircumstances), Δn in the range of 0.9 to 1.2 (preferably 1.1 orlarger), and Δε in the range of 6 to 12 (when the drive voltage is 7.5Vor lower, preferably 9 or larger. When the drive voltage is 10V orhigher, Δε may be in the range of 6 to 10).

[0262] Here, since the property constants of the liquid crystal materialsuch as Δn, Δε, and γ are correlating to one another, they can berealized by mixing various types of liquid crystal, the compound and thecomposition of which are not specifically limited.

[0263] In the above, various embodiments of the present invention aredescribed, and by arbitrarily combining those according to conditionsrelating to the panel structure, the material, the drive, and theperipheral circuits, the echo phenomenon can be suppressed at lowercots.

[0264] Here, described in the above various embodiments is the liquidcrystal display apparatus, but in any display device for driving pixelswith AC drive may also cause an echo phenomenon similar to the oneoccurring in the liquid crystal display apparatus. In this point ofview, the present invention is not limitedly applicable only to theliquid crystal display apparatus, but is widely applicable to anydisplay devices operating under AC drive.

INDUSTRIAL APPLICABILITY

[0265] As described in the above, with the present invention, an echophenomenon can be prevented and moving image display with higher qualitycan be realized even in display devices varying in type typified byliquid crystal display apparatuses which occur the echo phenomenon whendisplaying moving images, and degrade those when displayed.

1. An image display apparatus for displaying an image based on an inputvideo signal, comprising: a display device for outputting image lightsaccording to a voltage to be applied; drive means for driving saiddisplay device by switching the drive voltage between positive andnegative for application based on said input video signal; and means forsuppressing a polarization phenomenon in said display device.
 2. Theimage display apparatus according to claim 1, wherein said means forsuppressing the polarization phenomenon is adjustment means foradjusting said drive voltage by correcting said input video signal orsaid drive voltage so that absolute values of said drive voltage betweenpositive and negative become closer in at least any two successiveframes.
 3. The image display apparatus according to claim 2, whereinwhen an absolute value of the drive voltage in an n-th frame of a signalbeing normal to said input video signal is different from an absolutevalue of the drive voltage in an n+1-th frame or in an n−1-th frame,said adjustment means adjusts the drive voltage of any one of the n+1-thframe, the n−1-th frame, or the n-th frame.
 4. The image displayapparatus according to claim 3, wherein said adjustment means adjustsboth of said n+1-th frame and said n−1-th frame.
 5. The image displayapparatus according to claim 3, wherein when adjusting said drivevoltage, said adjustment means holds a maximum value or a minimum value.6. The image display apparatus according to claim 3, wherein whenadjusting said drive voltage, said adjusting means holds a sum of theabsolute values or a square sum of the absolute values of said n+1-thframe, said n−1-th frame, and said n-th frame.
 7. The image displayapparatus according to claim 2, wherein in the two successive frames thepolarity of the drive voltage applied thereto is different from eachother, said adjustment means adjusts said drive voltage to make adifference of the absolute values of the drive voltage to be ½ of amaximum drive voltage or smaller.
 8. The image display apparatusaccording to claim 7, wherein said adjustment means adjusts said drivevoltage to make said difference of the absolute values of the drivevoltage to be {fraction (1/10)} of the maximum drive voltage or smaller.9. The image display apparatus according to claim 8, wherein saidadjustment means adjusts said drive voltage when, prior to adjustment,said difference of the absolute values of the drive voltage is exceeding{fraction (1/10)} of the maximum drive voltage.
 10. The image displayapparatus according to claim 1, wherein said drive means divides onevertical scanning period of said input video signal into a first subperiod and a second sub period, and the drive voltage applied to the subperiods is different in polarity.
 11. The image display apparatusaccording to claim 10, wherein said drive means outputs the same videosignal in said first sub period and said second sub period.
 12. Theimage display apparatus according to claim 10, wherein said first subperiod and said second sub period are the same in length.
 13. The imagedisplay apparatus according to claim 10, wherein said first sub periodand said second sub period are not the same in length.
 14. The imagedisplay apparatus according to claim 10, wherein said drive meansincludes division means f or dividing said one vertical scanning periodof said input video signal into said first sub period and said secondsub period.
 15. The image display apparatus according to claim 14,wherein said division means includes means f or temporarily storing saidinput video signal.
 16. The image display apparatus according to claim14, wherein said division means includes means for delaying said inputvideo signal by a length of time equal to or shorter than the onevertical scanning period.
 17. The image display apparatus according toclaim 14, further comprising conversion means for converting said inputvideo signal into a data display signal for driving said display device,wherein in a process for converting said input video signal into saiddata display signal, said conversion means divides said one verticalscanning period of said input video signal into said first sub periodand said second sub period.
 18. The image display apparatus according toclaim 1, wherein said drive means divides one vertical scanning periodof said input video signal into a first sub period and a second subperiod, and outputs said input video signal in said first sub period,and outputs a comparison signal in said second sub period.
 19. The imagedisplay apparatus according to claim 18, wherein said second sub periodis shorter than said f irst sub period.
 20. The image display apparatusaccording to claim 18, wherein the drive voltage in said second subperiod is a voltage of a pedestal level or lower when said displaydevice is a normally black type, and when said display device is anormally white type, a voltage of the pedestal level or higher.
 21. Theimage display apparatus according to claim 20, wherein said displaydevice is a normally black type, and said drive voltage in said secondsub period is 0V.
 22. The image display apparatus according to claim 18,wherein said drive voltage in said second sub period is applied to aplurality of scanning lines at one time.
 23. The image display apparatusaccording to claim 1, wherein said drive means scans, in an n-th frame,odd-numbered scanning lines for a data signal, and even-numberedscanning lines for a compensation signal, and scans, in an n+1-th frame,the odd-numbered scanning lines for the compensation signal, and theeven-numbered lines for the data signal.
 24. The image display apparatusaccording to claim 1, wherein during one vertical scanning period ofsaid input video signal, after sequentially scanning either ones ofodd-numbered scanning lines and even-numbered scanning lines, said drivemeans sequentially scans the scanning lines.
 25. The image displayapparatus according to claim 1, wherein said drive means applies thedrive voltage of the same polarity without polarity reverse to at leastany two successive frames.
 26. The image display apparatus according toclaim 25, wherein said drive means applies such a drive voltage asalternating the polarity for every two frames.
 27. The image displayapparatus according to claim 25, wherein said drive means applies thedrive voltage of the same polarity between any two successive framesonce for every n frames.
 28. The image display apparatus according toclaim 1, wherein said display device includes: liquid crystal; and anorientation film, and a combination of said liquid crystal and saidorientation film is a combination to make a voltage holding ratio 98% orhigher.
 29. The image display apparatus according to claim 1, whereinsaid display device includes: liquid crystal; and an orientation film,and as said means for suppressing the polarity phenomenon, said liquidcrystal includes 1 wt % or less of a CN compound, and said orientationfilm does not include a high polymer whose conjugated length is sevenatoms or more.
 30. The image display apparatus according to claim 1,wherein said display device includes: liquid crystal; an orientationfilm; and a pixel electrode and a common electrode for applying thevoltage to said liquid crystal, and at least a part of said pixelelectrode and said common electrode applies the voltage to said liquidcrystal only via said orientation film.
 31. The image display apparatusaccording to any one of claims 1 to 30, wherein said display deviceincludes: liquid crystal; and an electrode for applying the voltage tosaid liquid crystal, and a part of said liquid crystal is driven in astate that there is none of said electrode in the vicinity thereof. 32.The image display apparatus according to any one of claims 1 to 30,wherein said display device includes: liquid crystal; and a pixelelectrode and a common electrode for applying the voltage to said liquidcrystal, and said liquid crystal is driven by an electric field which isgenerated between said pixel electrode and said common electrode, and isalmost parallel to a substrate.
 33. The image display apparatusaccording to anyone of claims 1 to 27, wherein said display device ismade of a material with which an echo phenomenon easily occurs.
 34. Animage display method for displaying an image by driving a display devicebased on an input video signal, comprising: a drive step of driving saiddisplay device by switching a drive voltage between positive andnegative for application based on said input video signal; and anadjusting step of adjusting said drive voltage by correcting said inputvideo signal or said drive voltage so that absolute values of said drivevoltage between positive and negative become closer in at least any twosuccessive frames.
 35. An image display method for displaying an imageby driving a display device based on an input video signal, comprising adrive step of driving said display device by switching a drive voltagebetween positive and negative for application based on said input videosignal, wherein said drive step divides one vertical scanning period ofsaid input video signal into a first sub period and a second sub period,and the drive voltage applied to the sub periods is different inpolarity.
 36. An image display method for displaying an image by drivinga display device based on an input video signal, comprising a drive stepof driving said display device by switching a drive voltage betweenpositive and negative for application based on said input video signal,wherein said drive step divides one vertical scanning period of saidinput video signal into a first sub period and a second sub period, andoutputs said input video signal in said first sub period, and outputs acompensation signal in said second sub period.
 37. An image displaymethod for displaying an image by driving a display device based on aninput video signal, comprising a drive step of driving said displaydevice by switching a drive voltage between positive and negative forapplication based on said input video signal, wherein said drive stepscans, in an n-th frame, odd-numbered scanning lines for a data signal,and even-numbered scanning lines f or a compensation signal, and scans,in an n-th frame, the odd-numbered scanning lines for the compensationsignal, and the even-numbered lines for the data signal.
 38. An imagedisplay method for displaying an image by driving a display device basedon an input video signal, comprising a drive step of driving saiddisplay device by switching a drive voltage between positive andnegative for application based on said input video signal, whereinduring one vertical scanning period of said input video signal, aftersequentially scanning either ones of odd-numbered scanning lines andeven-numbered scanning lines, said drive step sequentially scans thescanning lines.
 39. An image display method for displaying an image bydriving a display device based on an input video signal, comprising adrive step of driving said display device by switching a drive voltagebetween positive and negative for application based on said input videosignal, wherein said drive step applies the drive voltage of the samepolarity without polarity reverse to at least any two successive frames.